Battery monitoring is achieved by a number of methods in order to provide information regarding the condition of the battery and also to assist in the charging operation of the battery. With the advent of portable computers and cellular telephones, the need for rechargeable batteries has seen a significant increase. The battery operated equipment has typically utilized NiCd technology, NiMH technology, or Lithium Ion technology. The chemistries associated with each of these technologies can vary such that different considerations must be evaluated. However, one of the fundamental pieces of information that is required in any type of monitoring operation is the amount of charge input to the battery and the amount of charge retrieved from the battery.
Typical charge/discharge circuits are configured with some type of sense resistor disposed in series with the battery which provides a voltage representing the current to or from the battery. The polarity of the voltage will determine the direction of current flow. These resistors are referred to as "sense resistors," which are relatively small resistors to reduce the power dissipation or energy loss therein. The voltage across the resistor is converted to current information and this current information utilized by the battery monitoring circuit to determine various aspects of the condition of the battery. One such application is described in U. S. Pat. No. 5,357,203, issued to Landau, et al., on Oct. 18, 1994, which is incorporated herein by reference, which discloses a battery monitoring circuit that includes a plurality of counters that are incremented or decremented, depending upon whether there is a charge operation or a discharge operation. These count values are then utilized for the purpose of determining conditions about the battery, such as the capacity of the battery, the discharge rate of the battery, etc. However, this is a multi-function part, which requires a relatively large number of pins and is fairly complicated. It is not necessary to have all of these functions included in a single chip. The reason for this is that a large amount of the processing can be done external to the chip and this processing can be altered to alter the actual monitoring operation. With a single chip monitoring circuit, the monitoring operation is relatively fixed due to the use of an internal microcontroller on the chip itself. For battery pack applications that require the display in the entire monitoring operation to be incorporated into the pack, a single chip solution is acceptable. However, when this information can be readily performed by an external CPU, then it is not necessary to incorporate all of the monitoring processing operation on the chip itself.